Assembly comprising an implantable part designed to be fastened to one or more bones or bone portions to be joined, and at least one screw for fastening the implantable part to said bone(s)

ABSTRACT

An assembly including an implantable part designed to be fastened to at least one bone or bone portions to be joined and at least one screw for fastening the implantable part to the at least one bone or bone portions. The implantable part includes at least one tapped hole and the screw includes a head designed to be engaged in the tapped hole. The tapped hole is cylindrical and includes at least one radial notch emerging in a surface of the implantable part through which the screw is designed to be engaged in the tapped hole. The radial notch produces an interruption in the tapping included by the tapped hole. The head of the screw is conical, with an apical angle of between 15 and 25°.

FIELD OF THE INVENTION

The present invention relates to an assembly comprising an implantablepart designed to be fastened to one or more bones or bone portions to bejoined, and at least one screw for fastening the implantable part tosaid bone(s). Said implantable part may in particular be a fasteningbase for fastening part of a joint prosthesis to a bone, in particular afastening base for fastening a glenoid to shoulder blade in a totalshoulder prosthesis; the implantable part may also be a cortical plateor any other piece of arthrodesis or osteosynthesis equipment.

BACKGROUND OF THE INVENTION

It is well known to use screws to fasten implantable parts such as basesused to fasten joint prosthesis components or cortical or similar platesserving to perform an arthrodesis or osteosynthesis of one or morebones.

A very traditional base or plate comprises smooth cylindrical holes inwhich the fastening screws are designed to be engaged. Each hole may beadjusted to the dimension of the screw designed to be engaged in thathole, thereby defining a single implantation direction of the screw, ormay have a diameter larger than that of the screw, to allow implantationof the screw in a plurality of implantation directions.

In the first case, the base of the plate has the drawback of imposing animplantation direction on the screw and therefore prohibitingimplantation directions other than that which is imposed. However,depending on the anatomy of the bone or condition of the patient, it maybe preferable to implant the screw in a different direction from that ofthe hole. In the second case, the base or plate does not rule outdefective positioning of the screw in relation to the bone(s) in whichit is implanted, in particular the risk of the screw emerging at a jointsurface of one or more of said bones.

It is also known to arrange a tapping in the hole and a thread on thescrew head, the thread of the screw engaging with the tapping of thehole. Such assemblies also have the drawback of imposing an implantationdirection on the screw determined by said engagement.

Furthermore, such assemblies have a noteworthy risk of unscrewing of oneor more screws over time under the effect of the repeated forcesundergone by the bone(s). To resolve this risk of unscrewing, variousaxial retention systems have been designed for the screws, which, ingeneral, have the drawbacks of being relatively expensive to manufactureand not always being very effective.

Patent application publications nos. US 2010/312286, US 2008/208259 andUS 2008/140130 illustrate various techniques of the prior art.

The present invention aims to resolve the aforementioned drawbacks.

The main aim of the invention is to provide an assembly as previouslymentioned, in which at least one screw can be implanted in animplantation direction chosen from among several possible implantationdirections, and in which the risk of unscrewing of that screw over timeis reduced.

Another aim of the invention is to provide an assembly in which the riskof defective positioning of a screw is ruled out, or preserving thepossibility of choosing from among several possible implantationdirections.

SUMMARY OF THE INVENTION

In the concerned assembly, in a known manner, said implantable partcomprises at least one tapped hole, and said screw comprises a headdesigned to be engaged in said hole.

According to the invention,

the hole is cylindrical and comprises at least one radial notch emergingat least in the proximal surface of said implantable part, i.e. in thesurface of said implantable part through which the screw is designed tobe engaged in the hole, said radial notch producing an interruption inthe tapping comprised by the hole;

the head of the screw is conical, with an apical angle comprised between15 and 25°, and

said head is threaded and the pitch of this thread is comprised betweenone third and one half the pitch of the thread making up the tapping ofthe hole, and the depth of the thread of that head is comprised betweenone half and two thirds of the depth of the pitch of the thread makingup the tapping of the hole.

The inventor took the opposite course to the fundamental teachings ofmechanics, by seeking to engage and jam a screw head with a differentshape from that of the hole designed to receive that screw. He was ableto determine that the combination of the aforementioned features made itpossible to obtain the dual advantageous result of (i) making itpossible to engage the screw in a plurality of implantation directions,and (ii) producing, at the end of screwing, effective jamming of thehead of the screw in the hole, of a nature to oppose any risk ofunscrewing.

The plurality of possible implantation directions of the screw results(i) from the presence of said notch, which locally interrupts thetapping of the hole and allows a slight deformation of said implantablepart at that hole, (ii) the specific conical shape of the head, and(iii) the lack of narrow engagement of the respective threats of thehead of the screw and hole during the first portion of the screwingphase; said effective jamming also results from (i) said possibility ofslight deformation allowed by the notch, (ii) the specific conical shapeof the head, which allows the respective threads of the head of thescrew and the hole to gradually interlock during the second portion ofthe screwing phase, and which performs that complete interlocking at theend of screwing.

Preferably, said apical angle is 20°.

The pitch of the thread of the head of the screw is preferably in thevicinity of one half the pitch of the thread of the tapping of the hole.

It was possible to determine these values as optimal to obtain saidplurality of implantation and jamming directions of the screw. Theyallow a possibility of angulation of the axis of the screw in relationto the axis of the hole that may reach 20°.

This axis of the hole may itself not be parallel to a reference plane ofthe implantable part, for example the general plane in which a corticalplate extends. This angulation of the hole is also added to theangulation of the screw made possible by that hole to allow asignificant angulation of the screw in relation to said general plane.

Preferably, said screw comprises a body and a bone screw thread extendsalong that body into the immediate vicinity of the head of said screw,below said head, such that the proximal end of said screw thread issituated, when the screw is in place on the implantable part, insidesaid hole.

The presence of said screw thread in the hole contributes to achievingjamming of the screw in the hole.

Preferably, said notch extends over the entire height of the hole.

Said slight deformation of the implantable part at that notch is thusmade completely possible.

Preferably, the hole comprises a plurality of notches.

According to one possibility, said notches may be present over theentire circumference of the hole, allowing an angulated orientation ofthe screw over the entire circumference. They may particularly beregularly distributed on that circumference.

According to another possibility, these notches are present on a firstsector of the circumference of the hole and absent on a second sector ofthe circumference of said hole.

An angulated orientation of the screw is thus prohibited on the side ofthe hole opposite that on which said second sector is located. Due tothis possibility for selective angulation of the screw, resulting fromthe arrangement of the notches in carefully chosen locations of theholes, an implantable part may be produced making it possible to protectagainst the risk of defective implantation of the screw, in particularthe risk of a screw emerging at a joint surface of one or more of thetreated bones.

This possibility may in particular be implemented on a shoulderprosthesis glenoid base, to orient an anchoring screw in the pillar ofthe coracoid and the pillar of the shoulder blade. This possibility mayalso be implemented on cortical plates whereof one end is designed to beimplanted near a joint surface formed by a bone, in particular on anupper humeral plate or a lower radial plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be well understood, and other features and advantagesthereof will appear, in reference to the appended diagrammatic drawing,showing, as non-limiting examples, several possible embodiments of theimplantable part-screw assembly to which it pertains.

FIG. 1 is a perspective view of the plate comprising a series of holesin which anchor screws for anchoring that plate are designed to bereceived;

FIG. 2 is an enlarged perspective view of one of the holes;

FIG. 3 is a front view of the hole;

FIG. 4 is a side view of a screw;

FIG. 5 is an enlarged perspective view of the head of said screw;

FIG. 6 is an enlarged side view of said head;

FIGS. 7 to 9 are partial cross-sectional views of the plate and thescrew, during three successive phases of placing the screw in the hole;

FIG. 10 is a developed view of the hole, with a diagrammatic indicationof the position of the turn of the thread of the screw according tothree angulations, showing an absence of screw thread jump;

FIG. 11 is a front cross-sectional view of part of a shoulder blade inwhich a base for receiving a glenoid has been implanted;

FIG. 12 is a sagittal view of the portion of the shoulder blade, alongthe axis of said base;

FIGS. 13 to 18 are front views of six possible embodiments of a holecomprised by the implantable part according to the invention;

FIGS. 19 and 20 are sagittal and anterior views, respectively, of theupper portion of the humerus on which a plate according to the inventionhas been placed;

FIG. 21 is a top view of a plate for the lower end of the radius, and

FIGS. 22 and 23 are top and side views, respectively, of said plate,after placement on a radius.

DETAILED DESCRIPTION OF THE EMBODIMENT OF THE INVENTION

FIG. 1 shows an assembly 1 comprising an implantable part 2 designed tobe fastened to one or more bones or bone portions to be joined, andseveral screws 3 for fastening said implantable part 2 to said bone(s).

For the purposes of a purely diagrammatic illustration, the implantablepart 2 has been shown in FIG. 1 as a rectangular plate with any shapewhatsoever. FIGS. 11 and 12 show that this implantable part may be abase 2 for fastening a glenoid to a shoulder blade 100 or a part forminga convex joint surface called “metaglene” or “glenosphere” (not shown);this implantable part may also be a humeral cortical plate 2 (cf. FIGS.19 and 20) or cortical plate for the lower end of the radius (cf. FIGS.21 to 23).

The plate 2 shown in FIG. 1 comprises a plurality of aligned holes 4,each of which is designed to receive a screw 3.

As shown more particularly in FIGS. 2 and 3, each hole 4 is cylindricaland tapped, and comprises six notches 5 extending radially, regularlydistributed around its circumference. These notches 5 extend over theentire thickness of the plate 2 and consequently interrupt the screwpitch of the tapping of the hole 4 over the entire height thereof. Theyare substantially U-shaped, i.e. each one forms two radial surfacesopposite one another and a rounded bottom connecting those two surfaces.

In reference to FIGS. 4 to 6, it appears that the screw 3 comprises aconical and threaded head 3 a, and a body 3 b provided with a screwthread 3 c adapted for bearing in a bone.

The apical angle of the cone defining the head 3 a is 20° (cf. FIG. 6).The pitch of the screw thread of that head 3 a is in the vicinity of onethird of the pitch of the tapping of a hole 4, and the depth of thescrew thread is in the vicinity of one half that of the pitch of thetapping of a hole 4.

The screw thread 3 d of the head 3 a is symmetrical, has flanks that maybe inclined between 45° and 75°, and has an identical depth over theentire length of the head. The screw thread may be a dual entry screwthread.

The bone screw thread 3 c comprised by the body 3 b of the screw extendsalong said body into the immediate vicinity of the head 3 a, and isinterrupted immediately below that head 3 a.

Each screw 3 is designed to be engaged in a hole 4 and to be screwed inthe bone(s) to which the plate 2 is designed to be fastened. The screws3 may be engaged in the holes 4 perpendicular to the plate 2, as shownby FIG. 1, or maybe placed in said holes 4 not perpendicular to theplate 2, as appears in FIGS. 7 to 9.

This possibility for the angulation of the screw 3, and therefore of aplurality of possible implantation directions of that screw, results (i)from the presence of the notches 5, which locally interrupt the tappingof the hole 4 and allow a slight deformation of the part 2 at that hole4, (ii) the aforementioned conical shape of the head 3 a, and (iii) theabsence of narrow engagement of the respective screw threads of the head3 a of the screw 3 and the hole 4 during the first part of the screwingphase, i.e. substantially at the position of the screw 3 shown in FIG.8.

From this position, and in a second portion of the screwing phase goingas far as the end of screwing position shown in FIG. 9, progressive andeffective jamming of the head 3 a occurs in the hole 4, of a nature tooppose any risk of unscrewing of the screw 3. This jamming results from(i) said possibility of slight deformation allowed by the notches 5, and(ii) the aforementioned conical shape of the head 3 a, which allows thegradual interlocking of the respective threads of the head 3 a and thehole 4 during said second portion of the screwing phase, and whichperforms the complete interlocking at the end of screwing.

It will also be understood in reference to FIG. 9 that the portion ofthe first turn of the bone screw thread 3 c can be located, in thatend-of-screwing position, inside the hole 4, thus contributing to thejamming of the screw 3 in said hole 4.

FIG. 10 shows the development of the hole 4 with three lines 10, 11, 12each representing the development of a turn of the screw thread 3 d ofthe head 3 a, for respective angulations of the screw 3 of 0°, 6° and12°. It shows that there is no screw thread jump.

In reference to FIGS. 11 and 12, it appears that the aforementioned base2 comprises a central anchor lug 15 and four holes 4 distributed aroundsaid lug 15, designed to receive screws 3 (only two of the four screws 4are placed on the illustrated base 2, for which placement is inprogress).

It appears that the axes of the holes 4 are not parallel to the axis ofthe lug 15, but rather inclined in relation to the axis, by 10° in theillustrated example. This angulation of the holes 4 is thus added to theangulation of the screws 3 made possible by those holes, so as to allowa significant angulation of the screws 3 in relation to a referenceplane perpendicular to the axis of the lug 15. In the illustratedexample, the total angulation of the lower screw 3 is 20° (10°angulation of the hole 4 in relation to said axis, and 10° angulation ofthe screw 3 in the hole 4). Owing to this possibility of significantangulation, the upper screw 3 and the lower screw 3 can be orientedoptimally for anchoring respectively in the pillar 101 of the coracoidand the pillar 102 of the shoulder blade.

FIGS. 13 to 16 show holes 4 having shapes and numbers of notches 5different from those described above. The hole 4 shown in FIG. 13comprises notches identical to those described above, but compriseseight instead of six. The hole 4 shown in FIG. 14 comprises only fournotches 5, also U-shaped, but much wider than those described above. Thehole 4 shown in FIG. 15 comprises six notches 5 with a half-circlesection. The hole 4 shown in FIG. 16 comprises eight such notches 5 witha half-circle section.

The hole 4 shown in FIG. 17 comprises five notches 5 regularly arrangedon a first sector in the vicinity of 240° and is provided withoutnotches on a second sector in the vicinity of 120°. Similarly, the hole4 shown in FIG. 18 comprises four notches 5 regularly arranged on thefirst sector in the vicinity of 180° and is provided without notches onthe second sector in the vicinity of 180°. The absence of notches 5 onsaid second sectors amounts to a rigidity of the implantable part 2 andcontinuity of the screw thread of the tapping of the hole 4 at saidsecond sectors, which results in an impossibility of orienting the screw3 on the sides of the holes 4 opposite those on which said secondsectors are located.

Implantable parts 2 may thus be designed whereof the risk of defectiveimplantation of a screw 3 is eliminated.

Thus, in reference to FIG. 19, it appears that a humeral plate 2 maycomprise, in the epiphyseal portion thereof, two side-by-side holes 4whereof the sectors facing the side opposite the epiphyseal end of saidplate 2 are provided without notches. Then, an excessive orientation ofthe screws 3 toward the epiphyseal cortical bone of the humeral head 103is prevented, as shown in FIG. 20, which avoids the risk of said screws3 emerging on the joint surface of the humerus. The third hole 4comprised by said epiphyseal portion also has a sector provided withoutnotches on the side of that hole opposite the epiphyseal end of theplate 2; said sector thus prevents the orientation of the screw 3engaged in that hole toward the humeral diaphysis. However, thepossibility remains of choosing the implantation direction of the screws3 in the other directions mentioned above.

FIG. 21 shows a plate 2 for a lower end of the radius, traditionallyhaving a widened distal portion 2 a. In that distal portion 2 a, aproximal series 21 of four holes 4 and a distal series 22 of three holes4 are arranged transversely. The holes 4 of the proximal series 21 eachcomprise six notches as described above, allowing a multidirectionalorientation of the screws 3. Each hole 4 of the distal series 22comprises a first sector having four notches 5, turned toward the distalend of the plate 2, and a second sector provided without notches,situated on the side of the hole 4 turned toward the side of saidproximal series 21.

As will be understood in reference to FIGS. 22 and 23, the screws 3engaged in the holes 4 of the distal series 22 may not be orientedtoward the distal end of the radius 104, which prevents any risk of saidscrews 3 emerging at the joint surfaces comprised by said radius 104.

It appears from the preceding that the invention provides an assembly 1including an implantable part 2 and at least one screw 3, having thedecisive advantages of making it possible to engage the screw 3 in ahole 4 of the part 2 in a plurality of implantation directions, and ofachieving, at the end of screwing, effective jamming of the head 3 a ofthe screw in the hole 4, of a nature to oppose any risk of unscrewing.Another decisive advantage of this assembly 1 is making it possible toeliminate the risk of defective positioning of the screw 3.

The assembly 1 according to the invention can be used on all anatomiesother than those previously mentioned, such as femur, tibia, elbow orfoot, and works irrespective of the material used, for example stainlesssteel or titanium.

The invention was described above in reference to embodiments providedas examples. It is of course not limited to these embodiments, but onthe contrary encompasses all other embodiments covered by the appendedclaims. In particular, the base 2 shown in FIGS. 11 and 12 can comprisemiddle holes 4 (i.e. the two holes 4 other than the upper hole and thelower hole visible in FIG. 12) provided without notches 5 on the sectorsthereof turned toward the outside of the base 2, thereby prohibiting thescrews from being oriented in implantation directions that risk causingthose screws to emerge outside the bone.

What is claimed is:
 1. An assembly comprising: an implantable partdesigned to be fastened to at least one bone or bone portions to bejoined, and at least one screw for fastening the implantable part to theat least one bone or bone portions, said implantable part includes atleast one tapped hole, and said screw includes a head designed to beengaged in said tapped hole; wherein: the tapped hole is cylindrical andincludes at least one radial notch emerging in a surface of saidimplantable part through which the screw is designed to be engaged inthe tapped hole,; said radial notch produces an interruption in thetapping comprised by the tapped hole; the head of the screw is conical,with an apical angle comprised between 15 and 25°, and the head isthreaded and the pitch of the thread includes between one third and onehalf the pitch of the thread making up the tapping of the tapped hole,and the depth of the thread of the head includes between one half andtwo thirds of the depth of the pitch of the thread making up the tappingof the tapped hole.
 2. The assembly according to claim 1, wherein saidapical angle is 20°.
 3. The assembly according to claim 1, wherein thepitch of the thread of the head of the screw is in the vicinity of onehalf the pitch of the thread of the tapping of the tapped hole.
 4. Theassembly according to claim 1, wherein said screw comprises a body and abone screw thread extends along that body into the immediate vicinity ofsaid head of said screw, below said head, such that the proximal end ofsaid screw thread is situated, when the screw is in place on theimplantable part, inside said tapped hole.
 5. The assembly according toclaim 1, wherein said notch extends over the entire height of saidtapped hole.
 6. The assembly according to claim 1, wherein said tappedhole comprises a plurality of said notches.
 7. The assembly according toclaim 6, wherein said notches are present over the entire circumferenceof said tapped hole, allowing an angulated orientation of said screwover the entire circumference.
 8. The assembly according to claim 6,wherein said notches are regularly distributed on that circumference. 9.The assembly according to claim 6, wherein said notches are present on afirst sector of the circumference of the tapped hole and absent on asecond sector of the circumference of said tapped hole.
 10. The assemblyaccording to claim 1, wherein said implantable part is a fastening basefor fastening part of a joint prosthesis to a bone.
 11. The assemblyaccording to claim 10, wherein said implantable part is a fastening basefor fastening a glenoid to shoulder blade in a total shoulderprosthesis.
 12. The assembly according to claim 1, wherein saidimplantable part is a cortical plate.
 13. The assembly according toclaim 12, wherein said implantable part is a superior humeral corticalplate.
 14. The assembly according to claim 12, wherein said implantablepart is an inferior radius cortical plate.